This invention relates generally to parachutes and paragliders. More particularly, it relates to ram-air type parachutes and paragliders that include a plurality of cells with at least one valve in at least one of the cells to inhibit deformation of the air wing structure.
Much like an airplane wing, a ram-air parachute possesses an airfoil that provides lift and allows the operator to control the direction, speed and rate of descent. The shape and rigidity of a parachute determine such flight characteristics. Generally, a ram-air parachute consists of an upper surface and a lower surface connected by a plurality of vertically attached ribs. A cell of the parachute is the part of the parachute between the upper and lower skins bordered by a rib on one side and an adjacent rib on the other. Much like an airplane wing, one of the purposes of these ribs is to help the wing to keep its shape and strength. Load bearing ribs support and distribute the weight of the user by bearing forces of the lines connecting the user to the parachute.
Generally a parachute has lightning holes cut into the ribs to reduce its packed bulk and keep it evenly pressurized when inflated. The holes in the ribs of a parachute are called crossports and allow the air to communicate or move from higher pressurized cells to lower pressurized cells. The parachute is pressurized by high pressure air entering inlets along the leading edge of the parachute. Some parachutes possess internal cross braces, usually in the form of diagonal pieces of fabric connecting the top of one rib to the bottom of an adjacent rib. These cross braces provide additional support to the canopy and maximize the surface area of the parachute.
What keeps a traditional ram-air parachute pressurized, therefore, is the constant flow of air into or against the air inlets of the parachute. On a normal ram-air parachute more airflow means more rigidity and less airflow means less rigidity, less airflow also means the parachute will shrink in size. The reason the ram-air parachute looses rigidity and size with less airflow is due to air spilling out of the leading edge. Loss of parachute rigidity occurs when the parachute is slowed for landing and can also occur when flying in turbulent air.
Operators generally will select a parachute that matches their skill level and desired performance characteristics. Performance generally increases as the parachute size is reduced, allowing the operator to fly a faster, more responsive parachute. When the parachute is slowed for landing, however, the parachute looses rigidity and shrinks further in size, reducing lift and increasing the stall speed of the parachute. In order to land safely, an operator must select a parachute having a sufficiently large surface area to ensure a safe landing speed, while possessing a small enough surface area so that the parachute possesses the desired performance characteristics.
Reduced stall speed during slow landings due to loss of rigidity and shrinkage is one problem associated with ram air inflated parachutes. Loss of rigidity may ultimately lead, however, to the parachute canopy collapsing which can lead to injury or death of the user. Should the canopy be allowed to lose sufficient rigidity, the parachute may collapse and greatly increase the vertical descent of the operator. Landing is a particular vulnerable time for the parachute user, where slow speed, ground induced turbulence and reduced recovery time increase the risk of canopy collapse.
In order to increase maneuverability, reduce the stall speed and increase safety, it is desirable for a parachute to maintain a positive pressure within the majority of cells. It is especially important when encountering slow speed conditions or turbulence. It is also desirable for the parachute to maintain rigidity and maximum lift capacity during slow speed maneuvers such as landing allowing the operator to select and safely fly smaller parachutes for increased performance.